Abuse resistant preform and container neck finish

ABSTRACT

A neck finish of a preform or container having a crystallized top sealing surface (TSS) for withstanding deformation from multiple use cycles. In a returnable and fillable container, the improved TSS has enhanced caustic stress crack resistance resulting in a more secure finish-closure seal and an extended container life (number of refill cycles).

TECHNICAL FIELD

The present invention is directed generally to plastic preforms andcontainers, and more specifically to a preform and container neck finishable to withstand the mechanical abuse and rigors of multiple usecycles, while maintaining a secure seal with a closure.

BACKGROUND OF THE INVENTION

Conventional manufacture of plastic (e.g., polyethylene terephthalate(PET)) containers employs an initial step of forming a substantiallyamorphous and unoriented parison or preform by an injection moldingprocess. The process of crystallizing the finish of such preforms issometimes used to thermally stabilize the dimensions of the finish, andin particular the finish threads, for high temperature applications suchas hot filling and pasteurization.

In hot filling and pasteurization applications, the sealed containerundergoes significant pressure changes, i.e., the pressure increase dueto filling with a heated liquid and immediate capping or the exposure toa high temperature sterilizing bath/spray, followed by a decrease inpressure (vacuum) as the product in the container cools. These internalpressure changes cause the threads on the cap to push up or down on thewarm threads of the finish, distorting the finish threads. If the warmfinish threads distort, the cap becomes loose and there is a loss ofproduct quality (e.g., exposure to the atmosphere and possiblecontamination) and/or leakage.

There is another class of cold-filled carbonated beverage containers,known as returnable/refillable containers (also known as refillablecontainers). As distinguished from one way or disposable bottles whichare intended for a single use (i.e., only one cycle of manufacture,filling, distribution, consumption and disposal), refillable containersare designed to withstand the rigors of multiple pressurized coldfilling and use cycles, including a hot caustic wash between each useand refilling. Refill containers are uncapped when cleaned (by the hotcaustic wash), so the finish threads are not exposed to the cappingforces at high temperatures, as previously described. However, refillcontainers are subjected to greater opportunities for mechanical abuse.Not only must they typically withstand at least ten cycles of re-use tobe commercially viable as refillable containers, but after each use theyare potentially subject to unintended conditions of storage, handlingand misuse by the consumer (e.g., filling with other liquids, crushing,and/or use for other purposes, such as a candle holder) which canseriously affect their ability to survive the intended number ofcommercial re-use cycles. In particular, refill containers have asubstantially unoriented and amorphous neck finish of relatively lowmechanical strength. As such, the finish can easily be nicked or dentedduring such uncontrolled handling by the consumer prior to their returnto the manufacture for cleaning and re-use. This denting of the neckfinish is a particular problem because the neck finish is one area ofthe container with particularly tight dimensional tolerances necessaryto ensure a tight seal with the closure. With carbonated beverages, atight seal is particularly important to avoid a loss of carbonationpressure which reduces product quality and/or shelf life. For thesereasons, refillable containers are subject to a leakage test afterrefilling and a substantial number of refillable containers are rejectedfor failure to withstand the leakage test.

It would thus be desirable to provide a neck finish for a refillablepressurized container able to withstand the rigors of multiple usecycles and maintain a tight closure seal. As always, the commercialviability of such an improved neck finish will be determined by therelative costs of materials, processing steps, and required apparatusfor achieving the improved finish.

SUMMARY OF THE INVENTION

In one embodiment of the invention, there is provided a neck finish of apreform or container for receiving a closure and adapted to withstandthe abuse of multiple use cycles without leakage failure. The neckfinish includes a thread, bead or snap-on mechanism for attaching theclosure, and an open upper end with a top sealing surface (TSS) whichforms a liquid tight seal with the closure, wherein the TSS iscrystallized.

The neck finish may be for a pressurized returnable and refillablecontainer. The crystallized TSS provides a more secure finish-closureseal, thus increasing the service life of the container. Preferably, thecontainer can withstand at least 10 refill cycles, including a hotcaustic wash at a temperature of at least 60° C. and pressurized fillingof at least 3 atmospheres, while maintaining a secure seal with theclosure. More preferably, the container can withstand at least 20, andstill more preferably at least 25 refill cycles.

The crystallized portion of the neck finish extend from the TSSdownwardly and terminates above the thread, bead or snap-on mechanism.The neck finish may be made of a crystallizable polymer selected fromthe group consisting of polyesters, polyolefins and polyamides. The neckfinish in one embodiment comprises polyethylene terephthalate homopolyeror copolymers. The neck finish may be injection molded. Apart from thecrystallized TSS which is rendered opaque, the remainder of the neckfinish may be substantially transparent. The refillable container may besubstantially transparent below the opaque TSS.

The neck finish of the container may engage a closure having a sealingfin or liner for engaging the TSS.

In another embodiment, a container is provided comprising a pressurizedreturnable and refillable container which is cold filled with acarbonated beverage, and able to withstand at least 10 refill cyclesincluding a hot caustic wash at a temperature of at least 60° C. andpressurized filling of at least 3 atmospheres, the container having aneck finish made of a substantially transparent, amorphous andunorientied crystallizable polymer, and a crystallized opaque topsealing surface (TSS).

The container may include a closure which forms a liquid tight seal withthe TSS. The polymer may comprise polyethylene terephthalate homopolymerof copolymers. The container can preferably withstand at least 20 refillcycles and more preferably 25 refill cycles.

In another embodiment, a method is provided of making a neck finish of apreform or container for withstanding the abuse of multiple use cycles.The method includes providing a neck finish having a thread, a bead orsnap-on mechanism for attaching a closure and above the attachingmechanism a top sealing surface (TSS) for forming a liquid tight sealwith a closure, the method including crystallizing the TSS.

The neck finish may comprise a substantially transparent, amorphous andunoriented crystallizable polymer and the TSS is heated to crystallizeand render the TSS opaque.

The neck finish may be for a pressurized returnable and refillablecontainer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further advantages of the invention may be betterunderstood by referring to the following description in conjunction withthe accompanying drawings in which:

FIG. 1 is a partial perspective view of a top end of a preform accordingto one embodiment of the invention, having a neck finish with acrystallized top sealing surface (TSS);

FIG. 2 is a partial perspective view of a top end of a container, blownfrom the preform of FIG. 1, and sectioned vertically into two halves,showing the neck finish of the container with a crystallized TSS;

FIG. 3 is a schematic illustration of one embodiment of a neck finishand closure;

FIG. 4 is a schematic illustration of another embodiment of a neckfinish and closure;

FIG. 5 is a schematic cross sectional view of one embodiment of apreform for making a refillable container;

FIG. 6 is a schematic elevational view of a 1.5 liter PET refillablecarbonated beverage bottle produced from the preform of FIG. 5, whichillustrates the blow molding process by showing a partially blownarticle formed as the preform is expanded to form the container.

DETAILED DESCRIPTION

In accordance with various embodiments of the invention, a neck finishof a preform or container is provided having a crystallized top sealingsurface for withstanding the abuse of multiple use cycles.

One exemplary embodiment of a preform and container having a neck finishwith a crystallized top sealing surface (TSS) according to the inventionis illustrated in FIGS. 1-6. FIGS. 1-2 show a sample preform having acrystallized TSS, and the resulting container finish having acrystallized TSS. FIGS. 3-4 show two examples of closures applied to thefinish, illustrating the seal between the crystallized TSS and interiortop surface of the closure. FIGS. 5-6 show cross sections of a preformand the resulting blow molded refillable container.

FIG. 1 shows the top end of a preform 10 including a tapered shoulderportion 16, an increased diameter capping flange 11, and above thecapping flange, a neck finish 14. The neck finish 14 includes exteriorscrew threads 15 and above the threads a top sealing surface 13. Theentire preform is substantially transparent, except for the top sealingsurface 13 which has been rendered milky white or opaque, due tocrystallization.

FIG. 2 is a cut away view of an upper end of a container formed from thepreform of FIG. 1. The container has been vertically sliced in half,producing a left half 20A and a right half 20B. As shown, the containerincludes an upper tapered dome or shoulder portion 21A, 21B, which hasbeen expanded by blow molding the corresponding section 16 of thepreform. The result is a substantial reduction in wall thickness andincrease in orientation. In contrast, the capping flange 11A, 11B andneck finish 14A, 14B have not been expanded, and retain the samedimensions as in the preform 10. Again, the entire refillable container20 is substantially transparent, except for the crystallized top sealingsurface 13A, 13B.

The TSS has been crystallized to improve its nick resistance anddurability. In a returnable/refillable container, the finish issusceptible to nicks, abrasion and wear through repeated usage. Thepresent invention is directed to crystallizing only the top sealingsurface of the finish in order to reduce the mechanical damage, such asnicks, abrasion, etc. during the return and refill cycles. Reducing themechanical damage to the finish will reduce or prevent carbonation lossand increase the service life of the container by providing a moresecure finish-closure seal. In particular, an improvement in causticstress crack resistance has been found, i.e., the ability to withstand10 returnable and refillable cycles (a hot caustic wash of at least 60°C. followed by pressurized filling of at least 3 atmospheres), morepreferably 20 cycles, and still more preferably 25 cycles, withoutleakage of the closure (see the TSS/closure leakage test describedbelow).

FIG. 3 illustrates schematically and in cross section a typical threadedclosure 52 applied to a container neck finish 14. The closure includes atop wall 53 and a depending annular skirt 54 extending down from the topwall. The interior wall of the skirt includes an internal thread 55 forengaging a complimentary external thread 15 on the container neckfinish. The closure may be made of, for example, polypropylene (PP)and/or polyethylene (PE) material. The closure further includes a liner56 covering at least a portion of the underside of the top wall whichengages the top sealing surface (TSS) 13 of the finish. The liner may bemade of, for example, ethylene vinyl alcohol (EVA) and/or athermoplastic elastomer material such as an olefin or styrene butadienestyrene (SBS). As shown, the liner is intended to provide a tighter sealwith the TSS. The carbonation pressure, illustrated by arrows 5 exertingan upward force on the closure liner, acts to push away (separate) thecap liner from the TSS of the neck finish. Maintaining a tight seal ofthe neck finish enclosure requires maintaining a sufficiently highdownward force exerted by the closure threads on the finish threads tomaintain a seal between the TSS and cap liner, effectively counteractingthe upward carbonation pressure. By providing a crystallized TSS 13, theTSS can withstand a higher capping force, as well as maintainingresistance to nick abrasion and wear due to repeated usage.

One measure of the improved seal provided by the crystallized TSS is toconduct a leakage test as is known in the art. The test for leakage isperformed in a “Secure Seal Tester” distributed by SecurePak, P.O. Box1210, Maumee, Ohio 43537, USA. The Secure Seal Tester (SST) is used forchecking thread integrity and a proper seal on glass or plasticcarbonated beverage containers that use an aluminum roll-on, twistcrown, or plastic cap. By detecting gas leakage, rather than liquidleakage, the SST gives more sensitive and accurate readings (seewww.secure-pak.com). According to one embodiment, if the containersample does not leak at 175 psi, then it passes the leakage test.

To perform the test, a finish is cut from a plastic bottle or preformand placed in a fixture. The fixture is placed in a water tank and ahose attached for increasing the internal pressure until the closureleaks (i.e., bubbles are seen in the tank) and the air pressure ofleakage is recorded. In one embodiment, a refillable two litercarbonated beverage container is leak tested at 175 psi for 60 seconds.If it can withstand this pressure and time, it passes the leakage test.The closure used in the test is the same closure as is used commerciallyfor the sample container.

FIG. 4 shows another embodiment of a closure 70 on a neck finish 14.Closure 70 includes a top wall 72 having an interior downwardlyextending annular sealing fin 74 (rather than a liner) for forming aliquid tight seal with the TSS 13 of the finish.

The TSS may be crystallized by any of the known methods used in the art.Generally, a finish portion may be thermally crystallized by placing thefinish portion adjacent a heating element, such as a radiant heater, ata suitable temperature and for sufficient time to crystallize thepolymer in the area of the TSS. For example, for a PET refillablecarbonated beverage container, the heater may be positioned in a rangeof about ⅜ to ½ inches from the TSS, the heater being in a temperaturerange of about 500 to 1250° F., and the crystallizing taking about 30 to75 seconds. Adjustments to the time and temperature can be made forother preform materials and preforms of varying dimensions, includingthe desired depth of crystallization of the TSS. In accordance with thepresent invention, it is intended to crystallize only the area of theTSS, above the threads of the neck finish. The crystallization may besubstantially uniform or graded (e.g., of decreasing crystallizationlevels moving away from the TSS).

A particular example of a refill preform and container will now bedescribed, this being one application in which a container neck finishis subjected to increased opportunities for damage, including cracking,at the TSS.

FIG. 6 shows a typical 1.5 liter PET refillable carbonated beveragebottle. Generally, the refillable container has a relatively thin andhighly oriented sidewall and a relatively low orientation and thickenedbase portion. This combination enables the container to withstand thedemands of multiple returnable/refillable cycles.

More specifically, the bottle 20 is of a unitary blow-moldedconstruction, including a bi-axially oriented hollow body having aclosed bottom end 26 and an open top end 12 with a neck finish 14,extending above a capping flange 11. The neck finish has external screwthreads 15 for receiving a screw-on closure (not shown). Between theneck finish and base is a substantially vertically disposed sidewall 25,including an upper domed shoulder portion 21 above a substantiallycylindrical panel portion 22 (as defined by a longitudinal center lineCL) of the bottle. The base 26 has a central outwardly-concave dome 23with a central gate portion 24, and an inwardly-concave chime 28including a standing ring on which the container rests. A radiallyincreasing outer base portion 30 provides a smooth transition from thechime 28 to the sidewall 22.

A preform of the type suitable for making the container of FIG. 6 isshown in FIG. 5. The preform 10 has the same open top end 12 andunexpanded neck finish 14 with threads 15, as the container 20. Thepreform has a substantially elongated tubular body portion, including atapered shoulder forming portion 16, a substantially cylindricalsidewall forming portion 17, and a thickened base forming portion 18,which tapers to a reduced thickness end cap 19. The cylindrical preformsidewall 17 has a thickness of about 6.1 mm and is stretched at anaverage planar stretch ratio of about 10:1 to produce a bottle sidewall(panel 22) of about 0.6 mm. The planar stretch ratio is the ratio of theaverage thickness of the panel forming portion of the preform to theaverage panel thickness of the bottle. The preferred planar stretchratio for polyester refillable beverage bottles of about ½ to 2.5liters/volume is about 7-14:1, and more preferably about 8-13:1. Thehoop stretch is preferably from 3-4:1 and the axial stretch from2-3.5:1. This produces a container sidewall panel with the desired abuseresistance, and an injection molded preform sidewall with desired visualtransparency. The sidewall thickness and stretch ratio selected arebased on the dimensions of the specific bottle, the internal pressure ofthe product (e.g., 3 atmospheres for beer, 4 atmospheres for softdrinks), and the processing characteristics of the particular material(as determined, for example, by the intrinsic viscosity).

FIG. 6 includes schematic profiles of the preform 10 prior to and duringexpansion to form the container 20. The preform body is placed in a blowmold cavity (not shown) and the area beneath the capping flange 11 isaxially and radially expanded to conform to the surface of the moldcavity. A stretch rod (not shown) axially extends the preform such thatthe preform end cap 19 is brought into engagement with the bottom of theblow mold cavity, centering the preform in the cavity. The axialextension of the stretch rod occurs simultaneously and/or sequentiallywith radial expansion in the preform. FIG. 6 shows an intermediatepartially expanded body 32 during the blow molding process. Asillustrated, the thinner preform sidewall 17 is more easily stretchedand thus undergoes greater stretch than the base 18, resulting in arelatively thin, highly oriented bottle sidewall 22 and much thicker andlow orientation base 26.

The 1.5 liter container of FIG. 6 is about 335 millimeters in height andabout 93.5 millimeters in widest diameter. The container has varyinglevels of crystallinity corresponding to the extent to which the bottlewall portion is stretched to produce strain-induced crystallization andoptionally heated to produce thermal-induced crystallization. The panelportion 22 is blown to the greatest extent and has the highest averagepercent crystallinity of 25-35%. The tapered shoulder 21 has an averagepercent crystallinity of 20-30%. In contrast, the substantially thickerand lesser blown base 26 has 0-2% crystallinity in the central gate 24,2-8% in the chime 28, and a range of crystallinity there between thedome 23. The outer base 30 has a crystallinity range between that of thechime 28 and the panel 22. The neck finish 14 is not expanded andremains substantially amorphous and unoriented, at 0-2% crystallinity.

To maintain transparency, below the TSS of the neck finish, any thermalinduced crystallinity should be at relatively low temperature, e.g.,contact with a mold at a mold temperature of 110-140° C. for PET. Thepercent crystallinity is determined according to ASTM D1505 as follows:

% crystallinity=[(ds−da)/(dc−da)]×100

where ds=sample density in g/cm³, da=density of an amorphous film of 0%crystallinity (for PET 1.333 g/cm³) and dc=density of the crystalcalculated from unit cell parameters (for PET 1.455 g/cm³).

A refillable container is generally substantially transparent to enablecontaminant inspection. In accordance with the present invention, thecrystallized TSS will not substantially affect contaminant inspection,and if necessary the TSS can be inspected for contaminants by anothermeasure, such as visually. One measure of transparency is the percenthaze for transmitted light through the wall (H_(T)) which is given bythe following formula:

H _(T) =[Y _(d)÷(Y _(d) +Y _(s))]×100

where Y_(d) is the diffuse light transmitted by the specimen, and Y_(s)is the specular light transmitted by the specimen. The diffuse andspecular light transmission values are measured in accordance with ASTMmethod D 1003, using any standard color difference meter such as modelD25D3P manufactured by Hunterlab, Inc. A commercial refillable containerwould generally have a percent haze (through the wall) of less than 15%,preferably less than 10%, and more preferably less than about 5%.

The orientable crystallizable materials useful in makingreturnable/refillable containers include thermoplastic polyestermaterials such as those based on polyalkylene and, in particular,polyethylene terephthalate (PET). PET is meant to include the use ofcopolymers of PET in which a minor proportion, for example, up to about10% by weight, of the ethylene terepthalate units are replaced bycompatible monomer units. Thus, as used herein, PET means PEThomopolymer and PET copolymers of the grades suitable for makingcontainers, which are well known in the art. For example, the glycolmoiety of the monomer may be replaced by aliphatic or alicyclic glycolssuch as cyclohexane dimethanol (CHDM). The dicarboxylic acid moietiesmay be substituted with, for example, aromatic dicarboxylic acid such asisopthalic acid (IPA).

The PET polymers may contain other compatible additives and ingredientswhich do not adversely affect the performance characteristics of thecontainer. Examples of such ingredients include thermal stabilizers,light stabilizers, dyes, pigments, plasticizers, fillers, anti-oxidants,lubricants, extrusion aids, residual monomer scavengers and the like.

The intrinsic viscosity (IV) affects the processability of the polymerresins. PET having an intrinsic viscosity of about 0.8 is widely used inthe carbonated soft drink industry. Resins for various applications mayrange from about 0.55 to about 1.04, and more particularly from about0.65 to 0.85. Intrinsic viscosity measurements are made according to theprocedure of ASTM D-2857, by employing 0.0050±0.0002 g/ml of the polymerin a solvent comprising o-chlorophenol (melting point 0° C.) at 30° C.

The preform for making the transparent refillable bottle should besubstantially amorphous, which for PET means up to about 10%crystallinity, preferably no more than about 5% crystallinity, and morepreferably no more than about 2% crystallinity. The substantiallyamorphous or transparent nature of the preform may alternatively bedefined by a percent haze (HT) of about no more than 20%, preferably nomore than about 10%, and more preferably no more than about 5%. Thesubstantially amorphous preform may be a single layer or a multi-layerpreform made according to well known injection molding processes.

A commercial refillable container can generally withstand at least ten(10) refill cycles and, more preferably twenty (20) refill cycles, whilemaintaining its aesthetic and functional features. A test procedure forsimulating such a refill cycle without leakage is described below.

Each container is subjected to a typical commercial caustic washsolution prepared with 3.5% sodium hydroxide by weight and tap water.The wash solution is maintained at a designated wash temperature of atleast 60° C. The bottles are submerged uncapped in the wash for fifteen(15) minutes to simulate the time/temperature conditions of a commercialbottle wash system. After removal from the wash solution, the bottlesare rinsed in tap water and then filled with a carbonated water solutionat 4±0.2 bar (4.0±0.2 atmospheres) to simulate the pressure in acarbonated soft drink container (CSD) and then capped and placed in a38° C. convection oven at 50% relative humidity for twenty-four (24)hours. This elevated oven temperature is selected to simulate longercommercial storage periods at lower ambient temperatures. Upon removalfrom the oven, the containers are emptied and again subjected to thesame refill cycle, until failure.

Although several preferred embodiments of the invention have beenspecifically illustrated and described herein, it is to be understoodthat variations may be made in the preform and container construction,materials, and method of forming the same without departing from thescope of the invention as defined by the appended claims.

1. A neck finish of a preform or container for receiving a closure andadapted to withstand the abuse of multiple use cycles without leakagefailure, the neck finish having a thread, bead or snap-on mechanism forattaching the closure, and an open upper end with a top sealing surface(TSS) which forms a liquid tight seal with the closure, wherein the TSSis crystallized.
 2. The neck finish of claim 1, for a pressurizedreturnable and refillable container.
 3. The neck finish of claim 2,wherein the container can withstand at least ten (10) refill cycles,including a hot caustic wash at a temperature of at least 60° C. andpressured filling of at least 3 atmospheres, while maintaining a secureseal with the closure.
 4. The neck finish of claim 2, wherein thecontainer can withstand at least twenty (20) refill cycles, including ahot caustic wash at a temperature of at least 60° C. and pressuredfilling of at least 3 atmospheres, while maintaining a secure seal withthe closure.
 5. The neck finish of claim 2, wherein the container canwithstand at least twenty five (25) refill cycles, including a hotcaustic wash at a temperature of at least 60° C. and pressured fillingof at least 3 atmospheres, while maintaining a secure seal with theclosure.
 6. The neck finish of claim 2, wherein the crystallized portionof the neck finish extends from the TSS downwardly and terminates abovethe thread, bead or snap-on mechanism.
 7. The neck finish of claim 2,wherein the neck finish is made of a crystallizable polymer selectedfrom the group consisting of polyesters, polyolefins, and polyamides. 8.The neck finish of claim 2, wherein the neck finish comprisespolyethylene terephthalate homopolymer or copolymers.
 9. The neck finishof claim 2, wherein the neck finish is injection molded.
 10. The neckfinish of claim 2, wherein the crystallized TSS is opaque and theremainder of the neck finish is substantially transparent.
 11. The neckfinish of claim 10, wherein the refillable container is substantiallytransparent below the opaque TSS.
 12. The neck finish of a container ofclaim 10 including a closure having a sealing fin for engaging the TSS.13. The neck finish of a container of claim 10 including a closurehaving a sealing liner for engaging the TSS.
 14. A container comprising:a pressurized returnable and refillable container being cold filled witha carbonated beverage, and able to withstand at least 10 refill cyclesincluding a hot caustic wash at a temperature of at least 60° C. andpressurized filling of at least 3 atmospheres; the container having aneck finish made of a substantially transparent, amorphous andunoriented crystallizable polymer, and a crystallized opaque top sealingsurface (TSS).
 15. The container of claim 14, including a closure whichforms a liquid tight seal with the TSS.
 16. The container of claim 15,wherein the polymer comprises polyethylene terephthalate homopolymer orcopolymers.
 17. The container of claim 16, wherein the container is ableto withstand at least 20 refill cycles.
 18. The container of claim 17,wherein the container is able to withstand at least 25 refill cycles.19. A method of making a neck finish of a preform or container forwithstanding the abuse of multiple use cycles, the method comprisingproviding a neck finish having a thread, bead or snap-on mechanism forattaching a closure, and above the attaching mechanism a top sealingsurface (TSS) for forming a liquid tight seal with the closure, themethod including crystallizing the TSS.
 20. The method of claim 19,wherein the neck finish comprises a substantially transparent, amorphousand unoriented crystallizable polymer and the TSS is heated tocrystallize and render the TSS opaque.
 21. The method of claim 20,wherein the neck finish is for a pressurized returnable and refillablecontainer.